type Day =
  | 'Monday'
  | 'Tuesday'
  | 'Wednesday'
  | 'Thursday'
  | 'Friday'
  | 'Saturday'
  | 'Sunday';

declare const day: Day;
let result = '0';

switch (day) {
  // 只处理了'Monday'，缺少其他值的判断，并且也没有default分支
  case 'Monday':
    result = '1';
    break;
}
console.info(result);